1. Field of the Invention
This invention relates to a glass substrate having a pyrolytic anti-reflective coating. More particularly, this invention relates to a combined coating stack that reduces reflection from the film side while providing an aesthetically neutral tint. Even more particularly, this invention is directed to a coating stack of an iridescence-suppressing interlayer and a multilayered anti-reflective coating stack which enhances the reduction in visible reflectance while improving the color properties of the coated glass article.
2. Summary of Related Art
Coatings on glass are commonly utilized to provide specific energy attenuation and light transmittance properties. Additionally, coatings are designed to reduce reflections from interfaces between individual coating layers and the glass when a plurality of coatings are applied onto a glass substrate. The coated articles are often utilized singularly, or in combination with other coated articles, to form a glazing.
The attributes of a coated glass substrate are dependent upon the specific coatings applied to the glass substrate. The coating compositions and thicknesses impart energy absorption and light transmittance properties within the coated article while also affecting the spectral properties. Desired attributes may be obtainable by adjusting the compositions or thicknesses of the coating layer or layers. However, adjustments to enhance a specific property can adversely impact other transmittance or spectral properties of the coated glass article. Obtaining desired spectral properties is often difficult when trying to combine specific energy absorption and light transmittance properties in a coated glass article.
Anti-reflective coatings on glass are utilized to reduce the surface reflection of optical components and to reduce the reflectance of an interface between optical media with different refractive indices. The reduction of visible reflection is achieved by the principle of optical interference. When light impinges on the air-film, film-film, and film-glass interfaces, a portion of the beam is reflected at each interface. By proper choice of thin film materials and thicknesses, the individual reflected light beams can destructively interfere thereby reducing the observed visual reflectance.
While anti-reflective coatings on glass substrates are capable of reducing the observed visual reflectance, the visible light that is reflected is often an undesirable non-neutral color when viewed at a 90 degree angle incident from the glass. For purposes of this invention, a neutral color is defined under the CIELAB color scale system with an a* value in the range of about 6 to about -6 and b* value in the range of about 6 to -6.
It would be advantageous to provide a coated glass article having a low visible light reflection with the reflected light being neutral in color.
It would be a further advantage to a color neutral anti-reflective coating that may be applied pyrolytically onto a glass substrate. A pyrolytic film enables the deposition of the film on-line, for example, in a float glass production process.